A nonaqueous electrolyte battery prepared by using a graphite material or a carbonaceous material which absorbs and releases lithium ions for a negative electrode is commercialized as a high-energy density battery for portable devices. In recent years, the practical use of a lithium metal oxide containing Ni such as LiNiaCobAl1−a−bO2 or LiNiaCobMn1−a−bO2 as a positive electrode active material, in place of LiCoO2 or LiMn2O4, has been proceeded in order to improve the energy density of batteries.
On the other hand, in the case of mounting the battery in a vehicle such as an automobile or a train, the positive and negative electrodes are required to be formed of a material excellent in chemical and electrochemical stability, in mechanical strength and in corrosion resistance in view of storage performance in high-temperature environments, cycle performance, and reliability of high power over a long time. Further, the positive and negative electrodes are required to be formed of a material having high performance in cold climates, high-output performance in a low temperature environment (−40° C.), and long life performance. On the other hand, from the viewpoint of improvement in safety, a nonvolatile and noncombustible electrolyte solution has been developed as a nonaqueous electrolyte; however, it has not yet been put to practical use because it is accompanied by a decrease in output performance, low-temperature performance, and long life performance.
As described above, in order to mount the lithium ion battery on a vehicle, the objective is to achieve high-temperature endurance, cycle life, safety, and output performance.
When a titanium-based oxide such as TiO2 or Li4Ti5O12 is used as a negative electrode instead of the graphite material or the carbonaceous material, the lifetime performance and safety of the battery are improved. However, the energy density is decreased. The decrease in the energy density of the battery is due to the fact that the negative electrode potential of the titanium-based oxide (vs. Li) is as high as about 1.5 V, the battery voltage decreases, and the capacity of the negative electrode is small. Therefore, in order to increase the capacity of the battery, it is necessary to use the titanium-based oxide having a high capacity and excellent in output performance and lifetime performance.